In a known apparatus, the bottles are placed on a conveyor and they occlude the beam of light transmitted by a source transverse to the path of travel of the conveyor and directed towards an assembly of detectors. Means are provided for determining one or several dimensions of the bottles as a function of the condition, (degree of illumination attenuation) of said detectors. Control means allow displacing the beam of light so that each detector is successively reached. The identification is then obtained through a comparison between said measured dimension or dimensions and one or several corresponding dimensions stored in a memory. In order that the measurement be accurate, the scanning movement of the beam of light is synchronized with that of the conveyor. The scanning and synchronizing means make the construction of the apparatus complex.